Methods and systems for purifying styrene feedstock comprising use of low palladium catalyst

ABSTRACT

Apparatus, methods and systems useful for removing phenylacetylene from crude styrene feedstock are disclosed. Generally the processes and systems comprise the catalytic reduction of phenylacetylene to produce styrene via injection of a phenylacetylene reducing agent, such as hydrogen. A phenylacetylene reduction catalyst preferred Wherein comprises palladium on a calcium aluminate carrier, wherein the catalyst comprises less than 0.3 weight percent palladium.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to purification and polymerizationof monovinyl aromatic compounds. In another aspect, the presentinvention relates to purification and polymerization of styrenemonomers. In even another aspect, the present invention relates toapparatus, systems and processes for removing contaminants from styrenemonomer feedstock. In yet another aspect, the present invention relatesto apparatus, systems and processes for reducing the amount ofphenylacetylene in a styrene monomer feed, wherein the apparatus,systems and processes comprise a catalyst generally having less than 0.3weight percent palladium.

[0003] 2. Description of the Related Art

[0004] In the manufacture of monovinyl aromatic polymer compounds andmore particularly in the manufacture of polystyrene, a first stepcomprises the reaction of benzene together with ethylene to formethylbenzene. Ethylbenzene is dehydrogenated in an EB Dehydro unit toform styrene monomers. The resulting styrene monomers are thenpolymerized, usually in the, presence of a polymerization initiator orcatalyst, to form polystyrene resin.

[0005] If the ethylbenzene is dehydrogenated one step too far, anundesirable side product, phenylacetylene, is formed. As a result, theproduct stream from the Dehydro unit contains styrene, ethylbenzene, andtrace amounts of phenylacetylene. The ethylbenzene can be easily removedby conventional processes, such as distillation, leaving styrene monomerand phenylacetylene. However, removal of phenylacetylene is much moredifficult and distillation does not suffice.

[0006] The presence of phenylacetylene in the styrene monomer feedstockhas undesirable consequences on the polymerization process. In afree-radical polymerization process, the presence of phenylacetylene hasdetrimental effects on chain length and polymerization rate because itis a poor chain transfer agent. In an anionic polymerization process,phenylacetylene consumes a stoichiometric amount of the catalyst, suchas, for example, butyllithium, wherein one molecule of butyllithium isremoved from the polymerization process by each molecule ofphenylacetylene. This loss of catalyst can lead not only to high costs,but also to difficulty in controlling the molecular weight of thepolymerized product, an increase in the concentration of low molecularweight polymer, and the presence of unreacted styrene in thepolystyrene. Residual styrene monomer, which is a suspected carcinogen,contributes to off-taste, odor, off-color and other degradation of thepolystyrene.

[0007] Clearly, the presence of phenylacetylene in a styrene monomerfeedstock has adverse effects on cost of polymerization, control of thepolymerization process, and the quality of the resulting polystyrene.

[0008] Catalytic attempts to decrease the level of phenylacetylene instyrene monomer streams have involved the injection of high levels ofhydrogen gas into the stream. The phenylacetylene is then reduced tostyrene. Unfortunately, any hydrogen present in stoichiometric excess ofthe phenylacetylene also results in a significant conversion of styreneback to ethylbenzene, thus causing a lower styrene concentration and alower conversion rate.

[0009] U.S. Pat. No. 5,156,816, issued to Butler et al., discloses asystem for purifying styrene monomer feedstock using ethylbenzenedehydrogenation waste gas. The system comprises a palladium catalyst ona theta-alumina carrier wherein the catalyst contains 0.3 weight percentpalladium.

[0010] In spite of advancements in the art, many PAR systems and methodsare inefficient and suffer from catalyst failure due to plugging orattrition of the catalyst. Methods and systems for purifying monovinylaromatic feedstock that do not suffer from the limitations of the priorart have not been described.

[0011] Thus, there is a need in the art for methods of efficientlyremoving phenylacetylene contaminant from aromatic polyvinyl feedstock,said methods utilizing pa catalyst that does not, fail due to attrition,fluidization, or other loss of activity.

[0012] There is another need in the art for a system of efficientphenylacetylene removal from aromatic polyvinyl feedstock.

[0013] These and other needs in the art will become apparent to those ofskill in the art upon review of this specification, including itsdrawings and claims.

SUMMARY OF THE INVENTION

[0014] It is an object of the present invention to provide methods ofefficiently removing a phenylacetylene contaminant from aromaticpolyvinyl feedstock wherein the methods comprise a catalyst that doesnot fail due to attrition or fluidization or other loss of activity.

[0015] It is another object of the present invention to provide a systemuseful for efficient removal of phenylacetylene from aromatic polyvinylfeedstock.

[0016] Thus, one embodiment of the present invention is directed tomethods of purifying crude styrene monomer feedstock. The methodscomprise use of a low palladium catalyst having less than 0.3 weightpercent palladium.

[0017] Another embodiment of the present invention is directed to asystem of purifying a crude styrene monomer feedstock. The systems ofthe invention comprise reducing the phenylacetylene levels of monovinylaromatic monomer feedstock in polymerization systems by the use ofeither a two-bed reactor, or a pair of catalyst reactors. Each bed orreactor has injection means for injecting a phenylacetylene reducingagent, such as hydrogen gas, into the monomer reaction stream to reducephenylacetylene into styrene. Generally the catalyst reactors comprise alow palladium catalyst having less than 0.3 weight percent palladium,preferably less than about 0.1 weight percent palladium.

BRIEF DESCRIPTION OF THE FIGURES

[0018]FIG. 1 is a schematic representation of a conventional PAR system.

[0019]FIG. 2 is a schematic representation of one embodiment of a PARsystem of the invention.

[0020]FIG. 3 is a schematic representation of another embodiment of aPAR system of the invention.

[0021]FIG. 4 illustrates the phenylacetylene removal activities of asystem, of the invention and a conventional system.

[0022]FIG. 5 illustrates the phenylacetylene removal activity of asystem of the invention before and after a water excursion.

DETAILED DESCRIPTION OF THE INVENTION

[0023] One embodiment of the present invention is directed to a processfor purifying crude styrene. Preferably the crude styrene is a styrenemonomer feedstock created by the dehydrogenation of ethylbenzene (EB).The purification process comprises decreasing the level ofphenylacetylene. (PA) contaminate in the styrene monomer feedstock bythe addition of a phenylacetylene reducing agent which reducesphenylacetylene to styrene. Preferably the reducing agent is hydrogen.The processes of the invention comprise subjecting crude styrenecontaining phenylacetylene contaminant to heat and raising thetemperature of the styrene to about 150° F. The heated crude styrene,containing high levels of phenylacetylene, is then subjected to aphenylacetylene reduction process by reacting hydrogen with thephenylacetylene in at least two separate catalyst beds, wherein each bedcomprises catalyst having an extremely low level of palladium (Pd).

[0024] Catalysts useful in the present invention generally contain fromabout 0.01 to less than 0.3 weight percent palladium, preferably fromabout 0.02 to about 0.2 weight percent palladium, and more preferablyfrom about 0.03 to about 0.1 weight percent palladium. In a particularlypreferred embodiment, the catalyst of the invention has about 0.03 toless than about 0.05 weight percent palladium.

[0025] In addition, the catalysts utilized in the present invention aredispersed on a calcium aluminate carrier and generally have a densitygreater than 50 lbs/ft³, preferably greater than about 55 lbs/ft³, morepreferably greater than about 60 lbs/ft³, and most preferably greaterthan about 62 lbs/ft³. In a particularly preferred embodiment, thecatalyst of the invention has a density of about 66 lbs/ft³.

[0026] The catalysts used herein do not suffer from catalyst lossresulting from attrition by fluidization. Thus, the catalysts utilizedherein will not fluidize in the processes and systems of the invention.Generally the catalyst used in the present invention has a minimumfluidization velocity of greater than about 0.05 feet/second, preferablygreater than about 0.1 feet/second, and a process velocity of a valueless than that of the fluidization velocity. A particularly preferredminimum fluidization velocity is about 0.125 feet/second, and aparticularly preferred process velocity is about 0.114 feet/second.

[0027] An example of a catalyst found to be particularly useful in thepresent invention is Catalyst 38-6. by Synetix. Catalyst 38-6 is aselective hydrogenation catalyst dispersed on a ceramic support made ofcalcium aluminate, and has about 0.03 to 0.04 weight percent palladium(about 300 ppm to about 400 ppm palladium), a density of about 66lbs/ft³, a minimum fluidization velocity of about 0.125 ft/s, and aprocess velocity of about 0.114 ft/s. Catalyst 38-6 is available in theform of cylindrical pellets having a diameter of about 3.4 mm and alength of about 3.2 mm to about 3.7 mm, and a mean vertical crushstrength of greater than about 50 kgf.

[0028] Other known hydrogenation catalysts might also be successfullyutilized in the present invention. Of particular interest are the metalsof Groups VIIB and VIII, the transition metals, including platinum,nickel, iridium, ruthenium, rhodium, osmium, and rhenium. Otherpossibilities include the aforementioned transition metals modified withGroup IB and IIB metals such as gold, copper, and zinc. Other catalystgeometries may also be utilized herein, for example, extruded sphericalpellets rather than cylindrical ones. In addition to calcium aluminatecarriers, other known carriers might be utilized, such as silica, andsodium alumina silicates. Most preferably, the catalyst utilized hereinis Synetix's Catalyst 38-6.

[0029] In the processes and systems of the present invention,phenylacetylene is reduced into styrene by addition of a phenylacetylenereducing agent, preferably hydrogen. The processes and systems of thepresent invention comprise the use of at least one of the followingsources of hydrogen: 1) pure hydrogen; 2) hydrogen provided by the ventgas from the EB Dehydro unit (advantageous because of its readyavailability); 3) hydrogen mixed with a diluent; and 4) hydrogen and acatalyst modifier such as carbon monoxide (CO), wherein the CO acts as acatalyst modifier to decrease the selectivity of the catalyst fromreduction of styrene, and to increase its selectivity toward thereduction of phenylacetylene. If the hydrogen is mixed with a diluent,one particularly advantageous diluent is nitrogen, generally at a ratioof N₂ to H₂ in the range of about 1:2 to about 4:1. Although the diluentpreferred herein is nitrogen, other diluents, such as fuel gas, may alsobe used with the present inventive process. If carbon monoxide is usedas a catalyst modifier, the levels of carbon monoxide are generallyabout 1000 to about 2000 ppm, preferably about 1700 ppm.

[0030] In addition to the reduction of phenylacetylene by means of purehydrogen, an inert diluent may be utilized to control the reaction ofstyrene and hydrogen in the reactors to the point that very littlestyrene reduction and a high level of phenylacetylene reduction areachieved. One source of hydrogen which can be used involves vent gasfrom the EB dehydrogenation process which has been already used in aheat exchanger of the system to preheat the crude styrene monomer priorto reaction in the first catalyst bed. The vent gas hydrogen can becombined with a pure diluent such as nitrogen gas supplied by means suchas a nitrogen gas pipeline, railroad or truck tank care; or even bottlednitrogen gas. A typical EB dehydro vent gas analysis reveals the ventgas comprises about 89% hydrogen, about 7% carbon dioxide, less than 1%carbon monoxide, and the remainder being mostly hydrocarbons such asmethane.

[0031] Referring now to. FIG. 1, there is provided a highly simplifiedschematic flow diagram representing a conventional styrene purificationand polymerization process. One possible placement of a phenylacetylenereduction system of the present invention is indicated therein by thePAR hexagon.

[0032] In FIG. 1, styrene monomer which has been created from thedehydrogenation of ethylbenzene is provided at valve V1 from where itflows into the crude styrene storage tank CST. Crude styrene flows fromthe storage tank CST via flow line F1 into a vent gas heat exchangerVGHE in order to raise the temperature of the styrene, and from thereinto an optional preheater PH. From the preheater the crude styrenepasses into the phenylacetylene reduction system. PARS where thephenylacetylene in the crude styrene is reduced to acceptable levels.From the PARS, the refined crude styrene then flows through flow line F2into the BT Column Preheater BTPH where the styrene temperature israised prior to being injected into the BT Column. In this column,benzene and toluene are distilled off and removed through the top. Therefined styrene then passes into the EB Column where ethylbenzene andxylene are removed.

[0033] The EB Column has a second output that contains the “heavies” andthe refined styrene monomer. These are flowed into the Finishing ColumnFC where the heavies are separated from the purified styrene. Theheavies are removed out flow line F3 and the purified styrene flowsthrough line F4 into the styrene polymerization reactors A, B and C. Theheavies removed from the finishing column comprise pre-polymerizedpolystyrene, indene, indane, and other heavies referred to as “tars”.

[0034] The styrene monomer is next polymerized in the three reactorpolymerization system ABC and finished polystyrene is removed asindicated at PS through flow line F5. Columns B and C are shown havingrecycle lines exiting the top of the columns to recycle unpolymerizedstyrene monomer back into column A.

[0035] Referring now to FIG. 2, there is provided a schematicrepresentation of several embodiments of a PAR system of the presentinvention. A first embodiment involves the injection of pure hydrogeninto crude styrene feedstock prior to the styrene entering reactorvessels, such as R1 and R2. The pure hydrogen may be injected eitherbefore the crude styrene passes through a static mixer, after the crudestyrene passes through a static mixer, or both. Another embodimentinvolves the injection of hydrogen and nitrogen as opposed to purehydrogen. The manipulation of valves V1 through V11, allows for theinjection of either pure hydrogen, hydrogen and nitrogen, or anycombination thereof, into the PAR process at the aforementioned points.

[0036] In FIG. 2, crude styrene flow line F1 leading from the crudestyrene tank CST flows through the vent gas styrene heat exchanger VGSand is controlled by means of flow control valve V1 in line F1. The flowof crude styrene through vent gas styrene heat exchanger VGS serves atleast two purposes. First, the exchanger brings the crude styrene crudeup to a temperature of generally about 150° F. which is sufficient toinitiate the phenylacetylene reduction process. A second purpose is toprovide an optional vent gas supply which serves as a possible hydrogensource for hydrogen injection into reactor R1 and reactor R2 via controlvalves V10, V11 and V5.

[0037] The crude styrene is passed from vent gas styrene heat exchangerVGS through valve V1, flows up through static mixer SM1 and into firstreactor vessel R1 containing catalyst bed C1. The crude styrene flowsupward through catalyst bed C1 and exits through flow line F2 and ispassed through valve V4 into second static mixer SM2, and then flowsinto second reactor R2 containing second catalyst bed C2.

[0038] Reactor vessels R1 and R2 may be any type of vessel known in theart but are preferably liquid-full, upflow catalyst reactors. Catalystbeds C1 and C2 may be of any type known in the art, such as a fixed bed,and preferably contain a cylindrical catalyst. Generally the catalyst ison a calcium aluminate carrier and is made up of less than 0.3 weightpercent palladium, preferably less than 0.1 weight percent palladium,and more preferably less than 0.05 weight percent palladium. In aparticularly preferred embodiment, catalyst beds C1 and C2 comprise acylindrical catalyst on a calcium aluminate carrier, wherein thecatalyst comprises about 0.03 weight percent palladium.

[0039] Pure hydrogen from hydrogen sources HS1 and HS2 are provided foreach reactor R1 and R2, respectively, and are controlled by valves V2and V3, respectively. Although HS1 and HS2 are shown as separatehydrogen supply source, HS1 and HS2 may be from the same single hydrogensource such as, for example, a hydrogen supply pipeline, railroad ortruck tank cars of hydrogen, or even bottled hydrogen.

[0040] From reactor R2, the purified styrene monomer stream flows viaflow line F3 to vapor liquid separator vessel VLS from which thepurified styrene monomer stream SM exits via flow line F4. The separatedvapors V exit vapor liquid separator vessel VLS through flow line F5 tobe recycled in the process at the appropriate points.

[0041] A third pure hydrogen source, HS3, may also be used to providehydrogen to the system. Hydrogen from hydrogen source HS3 may besupplied via flow lines F6 and F9 via valves V6 and V9, respectively, tothe crude styrene flow coming from the vent gas styrene heat exchangerVGS before the styrene flow enters static mixer SM1. Hydrogen fromhydrogen source HS3 may also be supplied to the styrene flow via flowline F7 through valve V7 after the flow has exited reactor R1 but beforeit has passed through static mixer SM2.

[0042] Yet another source of hydrogen which can be used in the presentinvention is vent gas from the EB dehydrogenation process. Analysis of atypical EB dehydro vent gas shows the contents therein to be about 89%hydrogen, about 7% carbon dioxide, less than 1% carbon monoxide, and theremainder mostly hydrocarbons such as methane. Generally the vent gashas been passed through vent gas heat exchanger VGS together with thecrude styrene at the time of preheating the crude styrene monomer. Thevent gas hydrogen can be combined with a pure diluent, such as nitrogengas supplied a nitrogen gas pipeline, railroad or truck tank care; oreven bottled nitrogen gas.

[0043] An inert diluent may be utilized to control the reaction ofstyrene and hydrogen in the reactors to the point that very littlestyrene reduction and a high level of phenylacetylene reduction areachieved. A preferred diluent is nitrogen. The nitrogen may be added tothe hydrogen coming from hydrogen source HS3 at either one or both ofthe sites at which hydrogen from H3 is added. The ratio of N₂ to H₂should be in the range of from 1:2 to 4:1, preferably about 1:1, diluentto hydrogen.

[0044] If nitrogen is used herein as a diluent, it may be provided bynitrogen source N2. The nitrogen gas from source N2 flows through flowline F8 controlled by valve V8. The nitrogen may then be combined withthe hydrogen from source HS3, and the combination injected into flowline F9 via valve V9, at which point it is added to the crude styrenecoming from vent gas heat exchanger VGS. The nitrogen, hydrogen andcrude styrene are then mixed in static mixer SM1 to provide a thoroughmixing of the gases and the crude styrene feedstock before enteringreactor R1. A combination of nitrogen and hydrogen may also be suppliedto the styrene flow via flow line F7 via valve V7 prior to the styreneflow entering static mixer SM2. The mixture of hydrogen and nitrogen isinjected into the styrene flow and subjected to the action of staticmixer SM2 to provide a thorough mixing of the gases and the crudestyrene feedstock before entering reactor R2. Preferably, a diluent gassuch as nitrogen is utilized only in the first react or bed R1, but maybe utilized in both reactors R1 and R2 if desired.

[0045] Alternatively, instead of mixing the hydrogen with a diluent gas,the hydrogen may be mixed with a catalyst modifier such as, for example,carbon monoxide (CO). Generally the CO is supplied to the PAR system inthe EB dehydro vent gas in amounts of up to less than about 1%, andpreferably around 0.01 up to about 0.2%, but may also be supplied by anindependent source and mixed with pure hydrogen. The synergistic mannerin which the carbon monoxide and hydrogen interact in the presentinvention is unexpected because CO normally acts as a “poison” toprecious metal catalysts. Surprisingly, however, in the presentinvention the CO does not poison the catalyst but may provideselectivity of hydrogenation of towards phenylacetylene and away fromstyrene. Although not wishing to be limited or bound by theory, it ispossible that the CO does not permanently bond to the catalyst surfacebut instead, blocks those activation sites selective toward styrenewhile leaving available those sites active toward phenylacetylene. Thechange may involve changing the electronic configuration of the surfaceof the metal or the electronic environment thereon.

[0046] Thus the present invention involves the use of either purehydrogen as a reducing agent, hydrogen provided-by means of EB vent gas,hydrogen mixed with a nitrogen diluent, or the use of hydrogen andcarbon monoxide wherein the CO acts as a catalyst modifier to decreasethe selectivity of the catalyst from reduction of styrene and toincrease its selectivity toward the reduction of phenylacetylene.Preferably the hydrogen source of HS1 and HS2 is vent gas.

[0047] The initial level of phenylacetylene in crude styrene is in theamount of up to about 250 parts per million (ppm). After reaction in thePAR processes and systems of the present invention, the level ofphenylacetylene in the crude styrene feedstock is preferably less thanabout 10 parts per million.

[0048] Referring still to FIG. 2, the purified styrene monomer is thenflowed through flow line F3 to the vapor liquid separator VLS where thediluent gas and any possible remaining hydrogen gas (designated F5) areseparated through vapor line V. The crude styrene feedstock comprisingabout 61% styrene and 39% ethylbenzene (designated SM) are flowed fromvapor liquid separator VLS through styrene monomer line F4. From herestyrene monomer line F4 may connect with a benzene/toluene column, suchas column BT indicated in FIG. 1, where traces of benzene and tolueneare separated from the feedstock. Ethylbenzene is then removed from thestyrene in an ethylbenzene column located downstream of thebenzene/toluene column, such as column EB in FIG. 1, and the finalrefining step of the styrene monomer is accomplished in a finishingcolumn, designated FC in FIG. 1.

[0049] Referring now to FIG. 3, there is provided yet another embodimentof the present invention. In this embodiment, the two reactors R1 and R2of FIG. 2 have been replaced with a single two-bed reactor havingcatalyst beds B1 and B2 comprising cylindrical catalyst of a calciumaluminate carrier with a palladium metal having preferably less than 0.3weight percent palladium. A particularly preferred catalyst is Synetix'sCatalyst 38-6 In the embodiment provided in FIG. 3, crude styrene entersthrough flow line F10 passing through vent gas styrene heat exchangerVGS and into static mixer designated SM3. From there the styrene flowsinto the reactor R passing first through catalyst bed B1 and thenthrough catalyst bed B2. Vent gas from vent gas heat exchanger VGS isprovided via flow line F11 through various valve means into three pointsin the PAR system, one point being prior to static mixer SM3, the secondpoint being downstream of static mixer SM3 and the third point being inthe central area of the reactor R between catalyst beds B1 and B2.

[0050] Hydrogen from hydrogen source HS10 may be supplied by flow lineF12 and, as discussed above for the various hydrogen sources of FIG. 2,may be mixed with either carbon monoxide from a CO source, or withnitrogen from nitrogen source N2 through flow line F13 or it may beinjected directly into the reactor either upstream or downstream ofstatic mixer SM3, or in the central area of reactor R, by manipulationof the various valves in the various flow lines.

[0051] The present invention prevents the reduction of styrene andphenylacetylene to ethylbenzene, and involves the use of multipleinjection points, either by utilization of two reactors or of a two-bedsingle reactor. As disclosed herein, embodiments of the presentinvention utilize diluents, such as nitrogen, to slow the contact ofhydrogen with the styrene monomer stream constituents. Other embodimentsuse a hydrogen gas combined with a catalyst modifier such as carbonmonoxide to increase the selectivity toward phenylacetylene reduction.

[0052] The apparatus, processes, and systems of the present inventionare successful in reducing phenylacetylene levels in styrene monomerstreams from an undesirable level of up to 250 parts per million down tohighly desirable levels of less than about 10 parts per million.Although not intending or wishing to be bound by theory, it is possiblethat the reason for such a high success ratio with the present inventionis due to a combination of the chemistry involved as well as thegeometry of the catalyst which allows the hydrogen and thephenylacetylene to come together to react.

[0053] The present invention also reduces the energy required toinitiate the phenylacetylene reduction process. By use of the presentinvention, initializing the phenylacetylene reduction process canprimarily be accomplished by use of the inherent heat content of thestyrene feed at 150° F. from the VGS heat exchanger.

[0054] Generally the reactor pressure is operated at about 45 to about90 psi inlet pressure, preferably about 50 to about 85 psi, morepreferably about 60 to about 80 psi, and most preferably about 70 toabout 75 psi In the case of a two-reactor system, with an initialphenylacetylene concentration of about 200 ppm, a hydrogen tophenylacetylene ratio of about 16 to 1 is split equally between eachreactor. Likewise, in the two-bed reactor system with the dual injectionlocations, a 16 to 1 ratio of hydrogen to phenylacetylene is splitequally between the two points. Although other ratios of hydrogen tophenylacetylene may be-utilized herein, a 16 to 1 ratio provides-optimalphenylacetylene reduction and low conversion of styrene back toethylbenzene.

[0055] A desirable flow rate through the reactor system for the presentinvention is in the range of about 10 to up to 240 LHSV. Although anLHSV in the range up to 240 will work in the present invention, thepreferred LHSV rates are in the range of about 20 to about 120, becausethe higher rates are believed to contribute to shorter catalyst life.Preferably the overall LHSV rate is about 60, more preferably about 30.

[0056] Generally the amount of styrene reduction, which is undesirable,by use of the present invention is a very low level of about 0.1% to0.2% of the styrene being processed. Because ethylbenzene is removedfrom the styrene monomer and recycled back into the dehydrogenationprocess to be converted back into styrene, the conversion of styrene toethylbenzene is not as detrimental to the process as is the presence ofphenylacetylene. The 0.1:%. to 0.2% loss of styrene through reduction toethylbenzene is negligible and very acceptable. By the use of themulti-bed reactor, lessor amounts of hydrogen can be used such that thelose of styrene through reduction drops to less than about 0.1% andphenylacetylene can be reduced to less than 30 parts per million,preferably less than about 10 parts per million.

[0057] All references cited herein, including research articles, allU.S. and foreign patents and patent applications, are specifically andentirely incorporated herein by reference.

EXAMPLES

[0058] The invention having been generally described, the followingexamples are provided merely to illustrate certain embodiments of theinvention. It is understood that the examples are not, intended to limitthe specification or the claims in any manner.

Example 1 Phenylacetylene Removal Activity of the Present Invention

[0059] The objective of this experiment was to compare thephenylacetylene removal (PAR) performance of the present inventioncomprising the Synetix Catalyst 38-6 (triangles) to that of aconventional PAR method comprising the Criterion 05PAS#2 catalyst(circles). The Synetix Catalyst 38-6 has about 0.03 to about 0.04 weightpercent palladium, is on a calcium aluminate carrier and has a catalystbulk density of about 66 lbs/ft³. The Criterion 05PAS#2 catalyst has 0.3weight percent palladium, is on a theta-alumina carrier, and has acatalyst bulk density of 50 lbs/ft³.

[0060] The experimental parameters were as follows: RX3 in the recyclemode Mode Upflow Pressure  125 psig LHSV   60 hr−1 Catalyst Volume   20ml as whole extrudates Reactor 1″ O.D., 9\16″ I.D., 1\4“ ThermowellHydrogen Rate 16\1 Molar H---2\PA, 13 sccm Recycle Rate   17 ml/minFresh Feed (FF) 60:40 Styrene:EB, TBC Free FF Rate 0.91 g/min (1.00ml/min) FF Composition  0.4 wt % PA (for 200 ppm PA in total ReactorFeed) Additive None Temperature 150° F. (65.5° C.)

[0061]FIG. 3 provides graphic representation of the outcome of thestudy. As can be seen in FIG. 3, the present invention comprisingSynetix Catalyst 38-6 outperforms a conventional method comprisingCriterion 05PAS#2 catalyst.

Example 2 Water Excursion Test

[0062] The objective of this test was to expose the Synetix Catalyst38-6 to free water under reaction conditions to determine if catalystactivity is lost. Water is a co-feed to the dehydrogenation process and,although the water is decanted upstream of the PAR reactor, it ispossible that plant upsets could cause contact between the catalyst andwater.

[0063] The experiment was performed under the same conditions used inExample 1. The process was performed until catalyst activity wasstabilized. Water was then injected and the fresh feed rate was stopped.Upon observing free water in the effluent, water injection was stoppedand normal fresh feed was resumed. It took several days to clear allwater from the system.

[0064]FIG. 4 provides graphic representation of the outcome of thisstudy. As shown in FIG. 4, the PAR activity of the present inventioncomprising Synetix's Catalyst 38-6 is not lost after a water excursion.

[0065] A sample of Synetix Catalyst 38-6 was also soaked in water forthree days. (The support material of Catalyst 38-6 is calcium aluminatea material used for concrete cement.) Both the dry Catalyst-38-6material and the water-saturated Catalyst 38-6 material had crushstrengths that exceeded the capability of the catalyst crush strengthtester which has a capacity of 20 lbs.

[0066] While the illustrative embodiments of the invention have beendescribed with particularity, it will be understood that various othermodifications will be apparent to and can be readily made by thoseskilled in the art without departing from the spirit and scope of theinvention. Accordingly, it is not intended that the scope of the claimsappended hereto be limited to the examples and descriptions set forthherein but rather that the claims be construed as encompassing all thefeatures of patentable novelty which reside in the present invention,including all features which would be treated as equivalents thereof bythose skilled in the art to which this invention pertains.

We claim:
 1. A system for decreasing the level of a contaminant in acrude styrene feedstock, the system comprising: a) a crude styrenesupply comprising an initial level of contaminant X, a crude styreneinput stream, and a crude styrene output stream, wherein said crudestyrene input stream is arranged to receive crude styrene from anethylbenzene dehydrogenation unit, wherein said crude styrene isproduced by dehydrogenation of ethylbenzene in said dehydrogenationunit; b) a hydrogen source arranged to inject a first portion ofhydrogen into the crude styrene output stream to produce stream B; c) afirst catalyst bed arranged to receive stream B, wherein the firstcatalyst bed comprises a first catalyst bed output stream, wherein thefirst catalyst bed comprises a first catalyst having from about 0.01 toless than 0.3 weight percent palladium, and wherein said first catalystbed output stream comprises a level of contaminant X less then saidinitial level.
 2. The system of claim 1 further comprising: d) a secondhydrogen source arranged to inject a second portion of hydrogen intosaid first catalyst bed output stream to produce stream C; and, e) asecond catalyst bed arranged to receive stream C, wherein the secondcatalyst bed comprises a second catalyst bed output stream comprising alevel of contaminant X less then said first catalyst bed output stream.3. The system of claim 2 wherein the first hydrogen source is purehydrogen, vent gas obtained from the ethylbenzene dehydrogenation unit,or a mixture of hydrogen and a diluent.
 4. The system of claim 3 whereinthe second hydrogen source is pure hydrogen, vent gas obtained from theethylbenzene dehydrogenation unit, or a mixture of hydrogen and adiluent.
 5. The system of claim 4 wherein the diluent is nitrogen. 6.The system of claim 4 wherein said second catalyst bed comprises asecond catalyst comprising from about 0.01 to less than 0.3 weightpercent palladium.
 7. The system of claim 6 wherein said first andsecond catalysts each comprise from about 0.03 to about 0.05 weightpercent palladium.
 8. The system of claim 6 wherein said first andsecond catalyst beds are in a single reactor.
 9. The system of claim 6wherein said first and second catalyst beds are each in a separatereactor.
 10. The system of claim 6 wherein said first and secondcatalysts are phenylacetylene reduction catalysts dispersed on a calciumaluminate carrier, and are the same catalyst.
 11. The system of claim 19wherein said contaminant X is phenylacetylene, and wherein said level ofphenylacetlyene of said second catalyst bed output stream is less than10 ppm.
 12. The system of claim 11 wherein said first and secondcatalysts are in the shape of cylindrical pellets.
 13. A method fordecreasing the level of a contaminant in a crude styrene feedstock, themethod comprising the steps of: a) admixing a portion of a firstreducing agent together with a first portion of crude styrene to producea stream A, wherein said crude styrene comprises an initial level of acontaminant X; b) contacting stream A with a first catalyst bedcomprising a first catalyst comprising from about 0.01 to less than 0.3weight percent palladium to produce stream B, wherein stream B comprisesa level of contaminant X less than the initial level of contaminant X.14. The method of claim 13 further comprising the steps of: c) admixinga portion of a second reducing agent together with stream B to producestream C; d) contacting stream C with a second catalyst bed comprising asecond catalyst comprising from about 0.01 to less than 0.3 weightpercent palladium to produce stream D, wherein stream D comprises alevel of contaminant X less than that of stream B.
 15. The method ofclaim 14 wherein said first and second catalysts each comprise fromabout 0.03 to about 0.05 weight percent palladium.
 16. The method ofclaim 14 wherein said first portion of crude styrene is a stream ofstyrene, wherein said crude styrene is produced by dehydrogenation ofethylbenzene in an ethylbenzene dehydrogenation unit, and wherein saidfirst and second reducing agents are obtained as vent gas from saiddehydrogenation unit.
 17. The method of claim 15 wherein said first andsecond reducing agents are hydrogen gas.
 18. The method of claim 16wherein said first and second catalyst beds are in the same reactorunit.
 19. The method of claim 16 wherein said first and second catalystbeds are each in a separate reactor unit.
 20. The method of claim 15wherein said contaminant X is phenylacetlyene, and wherein said level ofphenylacetylene of stream D is less than 10 ppm.